A: Allergy reports are based on the number of pollen grains
or mold spores measured in a cubic meter of air. The source of the pollen, including
tree, weed or grass, is also usually included in the report. According to levels
established by the National Allergy Bureau (NAB), tree pollens can range from
"low" (less than 15 grains per cubic meter) to "very high"
(more than 1500 grains). The high end for grass pollen is more than 200 grains
and more than 500 grains for weed pollen.

Q: What U.S. cities have a combination of being at a
low altitude, with dry and mild climates? For health reasons, we would like
to explore our best choices.

A: Cities that meet these criteria include Eureka, Los
Angeles (especially outside of the city center), Santa Barbara, San Diego and
San Francisco, all in California.

Each of these locations lies below 1,000 feet in elevation
and experiences an average annual precipitation of less than 30 inches, as well
as fewer than 10 days per year, on average, with a high temperature of 90°F
or above or a with a low temperature of 32°F or below.

Check out our online
weather almanac to find average highs and lows as well as monthly precipitation
for various U.S. cities.

(Answered by Sean Potter, a certified consulting meteorologist
and science writer in New York City, July 4, 2006.)

Q: If the healthiest relative
humidity is 35% to 40%, what U.S. cities or states are in that range?

A: The Southwest USA is where
the average annual relative humidity ranges between 35% and 40%, according to
the National
Climatic Data Center. This includes southern Nevada, southeast California,
southern Arizona, southwestern New Mexico and extreme western Utah and west
Texas. Major cities with an average annual humidity of less than 40% include
Las Vegas, Phoenix and Albuquerque.

(Answered by Chris Vaccaro of the National Weather Service
in Silver Spring, Md., June 21, 2006)

Q: I have Seasonal Affected Disorder. Where in the USA
can I go to get the longest hours of daylight in the winter?

A: Travel to the southernmost point in the lower 48, which
is Key West. Even on the city's shortest day of the year  the first day
of winter  there are over 10 and a half hours of daylight. Compare this
to a more northerly city like New York, which receives only about nine hours
of daylight on its shortest day in late December.

Hawaii, however, boasts the longest hours of daylight during
the winter for the entire USA, since it is much farther south than Key West.
Honolulu receives almost 11 hours of daylight on its shortest day of the year.

For the most summer daylight, go to Angle Inlet, Minnesota,
which is the northernmost point in the lower 48 states. Barrow, Alaska, is the
northernmost point in the entire USA, and it actually receives 24 hours of daylight
for much of the summer. I'm just not sure staying there would help your Seasonal
Affected Disorder, though, since the temperature may not be quite warm enough
even in the summer.

A: The common explanation is
to say that the air gets "thinner" with increasing elevation. The
atmosphere is filled with air molecules, mainly nitrogen and oxygen, with more
molecules near the Earths surface and fewer as you increase elevation.
Its harder to breathe at high altitudes because oxygen molecules are fewer
and farther between, meaning theres less oxygen with each breath.

Some mountain climbers require bottled oxygen to accommodate this lack of oxygen
at high altitude. Athletes unaccustomed to higher elevations, such as teams
visiting Denver, often require supplemental oxygen as well.

Q: Where is a good place to
take a summer vacation if you have asthma?

For asthma sufferers, the best
vacation spots are where there are no rapid changes in weather or temperature.
For example, Florida wouldn't be good because of the tropical storm season.
Although Arizona and New Mexico are dry, the extreme high temperatures aren't
good for chronic asthma sufferers. Good summer vacation spots would be the beaches
along the mid-Atlantic and New England coasts.

(Answered by Dr. Abraham Sanders,
a pulmonologist at the New York-Presbyterian Hospital/Weill Cornell Medical
Center in New York City, August 11, 2005.)

Q: Are there any links between sinus pressure headaches
and barometric pressure?

A: Changes in the air pressure,
caused either by the weather or by your going up or down in an airplane can
cause sinus or ear pain.

Fortunately, for most people,
most of the time, pressure changes causes only minor discomfort.

If your sinuses are stopped up
by a cold or allergies, air can become trapped in them. If the air pressure
decreases, the difference between the higher-pressure air trapped inside and
the lower pressure outside causes an outward pressure, which can cause pain.
Going up in an airplane or a fast elevator in a high building causes the pressure
around you to decrease. The opposite happens when you come down.

Changes in the weather also causes
the air pressure to change. The pressure decreases as a storm is moving in,
increases as a storm moves away. (Related:Understanding
air pressure)

The relations between air pressure
and health is quite complicated and many scientific questions remain. You can
learn more by going to a USATODAY.com story on weather-related
pain.

Q: What weather conditions
cause barometric pressure changes? I get headaches when the barometric pressure
starts rising or falling and if I knew what was coming I could take medication
to head off my headache.

A: "Barometric" pressure
is the same as air pressure because we use barometers to measure it.

Air pressure changes are caused
by storms, which are areas of low air pressure, moving across the country. Areas
of high pressure,which usually bring clear skies, can move in to change the
pressure. (Related:What's
happening inside highs and lows)

The air pressure also drops and
rises when a boundary between warm and cold air - a front - comes by.

In general, you should be ready
for the pressure to begin falling when the forecast is for bad weather, such
as rain or snow, to move in. Such a forecast can mean that a storm is heading
your way or that a front is expected to cross your area.

When the storm leaves, the pressure
will begin rising, but the rise is often not as quick as the fall. Still, it
could cause you problems.

You can get an idea of what's
going on by looking at weather map - known as a surface chart - showing areas
of high and low pressure and fronts, such as the one USATODAY.com publishes
and updates regularly. (Related:U.S.
surface chart) If you scroll down the page with our chart, you'll see a
legend explaining the symbols. Television weather maps also show areas of high
and low pressure and front.

(Answered by Jack Williams,
USATODAY.com weather editor)

Q: My wife recently got 'altitude
sickness' traveling to Telluride, Colo., which was cured by going back down
to Cortez. Where can I find a table of city altitudes on the web?

A: The U.S. Geological Web site
has a Geographic names information systems page on its Web site that enables
you to find the elevation and the latitude and longitude of places in the USA.
You'll find a link to this page from the USATODAY.com maps
and navigation page. Using the USGS site, I found that the elevation of
Telluride is 11,600 feet while Cortez is at an elevation of 5,914 feet.

Before going to high-elevation
locations again your wife might want to check with her physician. There are
medications that you can take that will help offset the effects, at least for
some people. But, of course with any medication you need to worry about interactions
with other medications or conditions and possible side effects. For more information,
you can go to the USATODAY.com Weather
and your health page and scroll down almost to the bottom, where you'll
find links to information on altitude sickness.

(Answered by Jack Williams,
USATODAY.com Weather Editor, 8-8-99)

Q: Do changes in barometric
pressure affect people? For instance, it sometimes appears to cause headaches
in sensitive individuals (like me). I often notice a headache coming on when
the weather is changing from a high to low or vice versa, or when it's about
to rain. Is this my imagination or what? I would certainly appreciate a reply.

Q: Do weather conditions,
such as humidity or barometric pressure, effect body parts causing arthritis
or other pain?

A: There seems to be no doubt
that changes in barometric pressure and humidity along with other weather factors
do affect people, but I've never been able to find much, up-to-date information
about this topic. It falls under the general topic of "biometeorology," or the
study of weather and climate on living things from plants to people.

Hippocrates, the great Greek
physician of around 400 BC, wrote about weather effects on people. Humidity
could have a direct effect on the skin, with the skin expanding slightly with
rising humidity and contracting when the air becomes drier. This could explain
why humidity changes are painful to people with scar tissue, especially people
who have had limbs amputated. Air pressure changes and temperature changes affect
people with rheumatoid arthritis. It's easy to imagine how pressure changes
could cause headaches, but I don't know exactly how.

The only two references I have
to the topic are: Weather and Health by H.E. Landsberg, published by
Doubleday Anchor in 1969, and Human Biometeorology: An Updated, Selected
Bibliography - 1995 published by the U.S. National
Climatic Data Center in 1985.